Oil sands ore, known as bituminous sands, comprises a naturally occurring mixture of sand, clay, water and bitumen. Oil sands ore may vary in quality and character from region to region, or deposit to deposit. Generally, Athabasca oil sands in Canada comprises water-wet sand grains, while Utah oil sands in the United States comprises oil-wet sand grains. The sand grains themselves may be of different composition.
Oil sand extraction processes are used to liberate and separate bitumen from oil sand ore such that the bitumen can be further processed to produce synthetic crude oil. Numerous oil sands mining and bitumen extraction processes have been developed and commercialized, all of which involve the use of water as a processing medium. One such water extraction process is the Clark hot water extraction process (the “Clark Process”), which was the first commercially successful oil sand extraction processes.
A water extraction process such as the Clark Process typically requires that mined oil sand be conditioned for extraction by being crushed to a desired lump size and then combined with caustic water to form a conditioned slurry of bitumen, water and minerals (sand and fine particles). In the Clark Process, the water used is heated to about 65 to 80° Celsius, and an amount of sodium hydroxide (caustic) is added to the slurry to adjust the slurry pH upwards, which enhances the separation of bitumen from the oil sand. Other water extraction processes may have other temperature requirements and may include other conditioning agents which are added to the oil sand slurry.
A bitumen extraction process will typically result in the production of a number of product streams, some of which are disposed of as waste. For example, in the Clark Process, these streams include a bitumen froth stream comprising of bitumen, sand, fine particulate mineral solids and water, a middlings stream comprising bitumen, fine particulate mineral solids and water, and a coarse tailings stream consisting primarily of coarse particulate mineral solids and water. The bitumen froth stream and the middlings stream are typically processed further, both to recover and purify bitumen and to render the fine solids more readily disposable and make them less of an environmental hazard. The coarse tailings stream is not typically processed further, since the coarse particulate solids are relatively easy to dispose of and do not typically present a significant environmental risk.
The bitumen froth stream is processed in a froth treatment process to separate water and fine grain size solids from the bitumen. The fine solids and water recovered from the bitumen froth stream are typically ultimately disposed of in tailings ponds, where long-term settling of the fine solids may take place and the water recovered and reused. Tailings management remains a significant environmental issue and processes which minimize tailings may be advantageous,
There remains a need for more efficiently separating bitumen and solids in an oilsand processing operation. There may be advantages in exploiting certain characteristics of different oil sands ores in order to more efficiently treat the ore to extract bitumen.